Plasma Physics Reports最新文献

A high-frequency jet discharge (1.76 MHz) at reduced pressure in a system with a liquid plasma-forming medium (6% aqueous solution of (NH₄)₂SO₄) has been studied experimentally. The morphology and stability of the discharge, its electrophysical, spectral, and thermal characteristics have been studied in the range of 1000–80 000 Pa. It is shown that the discharge transferred from a discrete microchannel structure to an extended truncated-conical column when the pressure decreased from close to atmospheric one to 20‒4 kPa. At ~1 kPa, non-stationarity and breakdown dynamics occur due to a decrease in the boiling point and intense vaporization. The current–voltage characteristics are plotted as Lissajous ellipses. Emission spectroscopy and the analysis of the Hα/Hβ Stark broadening show the electron density along the Hβ line. Infrared thermography records a local temperature maximum in the jet–plasma interaction zone. The results provide a “passport” for the modes and confirm the existence of an energy-efficient pressure range of 20‒40 kPa for plasma-liquid applications.

The capabilities of the ion velocity distribution function diagnostics based on recording collective Thomson scattering (CTS) spectra of microwave radiation are analyzed for the TRT (Tokamak with Reactor Technologies) project. This diagnostics can be used to study thermal ions, including determining the ion temperature, isotope composition, and effective charge of the plasma, and fast ions arising from plasma heating by neutral beams or fusion reactions. Possible scattering scenarios for a wide range of probing radiation frequencies from 70 to 400 GHz are considered. CTS scattering spectra are calculated for model parameters of the background plasma and fast ion distributions, the resolution and sensitivity of the CTS diagnostics are estimated, and requirements for the probing radiation source and receiving equipment are determined. Probing at a frequency of 82.6 GHz, corresponding to the lower boundary of the transparency window for the extraordinary wave of magnetized plasma, is optimal according to the analysis results. In this case, scattering is recorded at an angle close to a direct angle relative to the direction of propagation of the probing microwave beam. In this geometry, the analysis bandwidth of the scattered signal at the intermediate frequency is 0.1‒0.6 GHz for thermal ions and 0.8–3 GHz for fast ions. The possibility of using radiation at the frequency of electron cyclotron plasma heating is additionally considered. It is shown that plasma probing with the ordinary wave at a frequency of 230 GHz is possible; however, the sensitivity of this scheme drops by two orders of magnitude compared to the main one.

This paper presents the results of numerical simulations of the time evolution of plasma current and the suppression of the runaway electron current in an ITER-scale tokamak during the disruption of the tokamak discharge by means of injection of tungsten collectors capturing the runaway electrons (RE). A zero-dimensional approach was used while solving a system of two differential equations for both plasma and RE currents. The RE losses on the tungsten collector during its flight through the plasma at the discharge current quench stage were taken into account. Requirements were formulated for the selection of collector injection parameters ensuring the safe operation of the tokamak. The simulation results show that the most promising scenario is the simultaneous injection of three 80-gram tungsten collectors at a speed of 250 m/s immediately after the thermal quench stage.

A self-consistent model describing a glow discharge in argon with a liquid-phase (distilled water) anode is presented. The model is based on an extended hydrodynamic description of plasma and takes into account the heating of the metal cathode and liquid-phase anode, as well as the equilibrium evaporation of water molecules into the discharge gap and the kinetics of elementary processes involving them. A numerical study is performed for two key cases: the discharge initiation in a pure argon atmosphere and that with the initial presence of water molecules at a concentration corresponding to the saturated vapor pressure at an initial liquid-phase anode temperature of 293 K. For the first case, it is shown that a change in the plasma-forming ion from ({text{Ar}}_{2}^{ + }) to the hydrated cluster ({{{text{H}}}_{9}}{text{O}}_{4}^{ + }) ion and also a change in the dominant negatively charged particle from the electron to the OH^– ion are observed during the evaporation of water molecules. For the second case, it is shown that ({{{text{H}}}_{9}}{text{O}}_{4}^{ + }) is the dominant positive ion over the entire time interval. The competition between electrons and OH^– ions on times up to ~0.01 s was detected for negatively charged particles. The OH^– ion becomes the dominant negatively charged particle at times larger than 1 s but the electron density remains comparable by the order of magnitude, which is critical for maintaining plasma conductivity.

A thermal atmospheric plasma generated by an electrodeless microwave torch in an argon jet, which is placed within a protective nitrogen environment, is used to produce plasma-activated water (PAW). The aim is to prepare hydrogen peroxide and nitrous acid–based solutions for application in cancer and skin-disease therapy via indirect treatment methods. In these approaches, the activated water or the medium (PAM) prepared from it, which contains controlled concentrations of long-lived reactive oxygen and nitrogen species (RONS), can selectively affect transformed cells without injuring healthy ones. PAW produced by well-known non-thermal (cold) atmospheric plasma (CAP) sources based on electrode discharges typically contains metal impurities originating from the electrodes and moreover is produced only in limited quantities because of the low plasma density of such discharges. By contrast, PAW obtained using thermal atmospheric plasma has high purity and offers controlled levels of long-lived species, namely hydrogen peroxide (H₂O₂) and nitrite ions (NO₂^–), with concentrations exceeding 1 mM at pH ≈ 3. Batch volumes of 0.1–2 L can be produced with activation times up to 20 min.

Modern trends in tokamak design include the use of strong magnetic fields, whose generation produces Lorentz forces, which can damage the electromagnetic system (EMS) of the tokamak. A concept for the tokamak EMS is proposed that ensures reduced loads in the central region. Results of numerical simulations are presented, which substantiate the possibility of a significant reduction in mechanical stresses on the tokamak inductor through the use of quasi-force-free windings.

The paper considers the operational frequency range and spatial region accessibility of reflectometry for electron density fluctuation measurements in plasma column in the T-15MD tokamak. The absorption of the probing beam at the fundamental and higher harmonics of the electron cyclotron resonance is identified as the primary diagnostic limitation. The estimations were made for ordinary and extraordinary polarizations of the probing wave in a wide range of discharge scenarios. Configurations with different antenna locations inside the vacuum vessel are examined. The maximum fluctuation amplitude, under which the reflectometer works in linear regime, is assessed for the target density profile shape.

The characteristics of poloidal correlation fluctuation reflectometry diagnostics for a small-sized tokamak were studied using numerical simulations. The simulations were conducted using the method of fast synthetic diagnostics based on the linear (Born) scattering theory and including full-wave calculations of electric fields of microwaves in unperturbed plasma. The signal of microwaves scattering by density fluctuations was calculated in accordance with the reciprocity theorem using the data from gyrokinetic calculations of the space-time distribution of these fluctuations in plasma of the FT-2 tokamak. The frequency spectra of the synthetic scattering signals were compared with the spectra of density fluctuations in the scattering region obtained from gyrokinetic calculations. From synthetic scattering signals, radial profiles of the poloidal phase velocity of fluctuations were calculated and compared with similar profiles calculated directly from the gyrokinetic distributions of density fluctuations, as well as with the profiles of the poloidal E × B drift velocity of plasma.

The theory of Hall magnetohydrodynamics of rotating partially ionized plasma taking into account the effects of viscosity and thermal conduction is developed. The key supposition of the developed theory consists in the assumption that the temperature of each component of the partially ionized plasma is determined by the temperature of the neutral component. In fact, the neutral component plays the role of a heat bath for the charged components. Equations governing the motion of the center of mass of the partially ionized plasma that take into account the effects of viscosity and thermal conduction are derived. The developed theory describes convection processes in rotating partially ionized plasma. The obtained equations of the Hall magnetohydrodynamics are expressed in the Boussinesq approximation. The Bénart problem of the layer of rotating partially ionized plasma heated from below is formulated. The linear problem of hydrodynamic instability is solved, and the threshold and growth rate of the convective instability are found. The obtained threshold of the onset of instability of the layer of partially ionized plasma heated from below depends on the Taylor number, the Chandrasekhar number, along with the ratios of the Hall and ambipolar diffusion coefficients to the ohmic diffusion coefficient.

An experimental design is proposed for studying a thermal wave that occurs in plasma under large electron temperature gradients, when the proportionality between the heat flux and the temperature gradient is violated. The heat flux becomes nonlocal under these conditions, i.e., it depends on the distribution of plasma parameters in a certain volume. Existing models for describing heat flux give conflicting predictions for some problems, so a more accessible experimental setup is needed for studying heat transfer in the laboratory and verifying numerical codes. The experimental setup proposed in this work minimizes the influence of hot electrons of another nature and distinguishes between radiative preheating. The effect under study is important in the development of certain laser thermonuclear fusion schemes, as well as in experiments with a significant energy input into the plasma.